338 M. Arfwedson on the Decomposition of [May, 



residue when heated gave out sulphur, and oxide of cobalt 

 remained. 



2. 0*379 gr. of this reduced substance, treated with sulphu- 

 retted hydrogen gas, gave out water, and the weight at the 

 conclusion of the process was 0*440 gr. In a subsequent expe- 

 riment the weight was increased from 0*224 to 0*261 gr. The 

 number 0*440 corresponds with 116*09 to the 100 parts, and 

 the number 0*261 with 117*04. The water obtained in this pro- 

 cess, together with what was said above of the presence of 

 sulphur, shows us that the sulphate of cobalt decomposed by 

 hydrogen gas becomes likewise an oxisulphuret. 



The residue per cent, when the salt is reduced, amounts in the 

 first experiment to 53*99 ; and in the second to 53*24 ; or at a 



medium to 53*62: but 2 Co & : Co + Co S' 2 :: 100 : 53*55. 

 From this we may conclude, that sulphate of cobalt is decom- 

 posed by hydrogen gas in the same way as protosulphate of 

 manganese ; or that one-half of the salt is converted into oxide, 

 and the other half into sulphuret. The experiments with sulphu- 

 retted hydrogen gas ought to have corresponded with the fore- 

 going result ; but this is not the case ; for the weight of Co + 

 Co S 2 : 2 Co S°- :: 100 : 109*7 ; consequently from 100 parts of 

 the oxisulphuret I should have obtained 109*7 of sulphuret, 

 whereas in the experiments I got as much as 117*04 ; but I have 

 good reasons for presuming that this experiment formed a sul- 

 phuret containing more sulphur than Co S a . Since the cobalt 

 pyrites from Riddarhyttan, according to Hisinger's analysis,* 

 consists of cobalt united to three atoms of sulphur. The number 

 1 17*04 agrees nearly with Co S 2 + Co S ; . 



Sit/phate of Nickel. 



A portion of pure oxalate of nickel (obtained according to 

 Laugier's method, by adding oxalic acid to a solution of nickel 

 not free from cobalt in ammonia) was heated in a small retort 

 till it was decomposed. The residual metallic nickel was 

 dissolved in dilute sulphuric acid, and evaporated till it yielded 

 crystals. 



1*015 gr. of crystallized sulphate of nickel freed from moisture 

 by exposure to heat,i" were treated with hydrogen gas. This 

 salt was decomposed as easily a»d speedily as the preceding 

 salts. At first sulphurous acid and water were evolved, but at 

 last the gas which came over had the odour of sulphuretted 

 hydrogen. After an hour, even this odour ceased, and the 

 apparatus was allowed to cool. The residue of this experiment 

 weighed 0*49 gr. and was a pale-yellow cohering mass, which 



« Afhandl. i Fysik, Keuii, &c. iii. 310. 



•j- This must be done with caution, because the salt begins to be decomposed at a 

 cherry-red heat. 



